Most continuous casting installations for steel in operation today have a generally vertical mold followed by a guide for the strand or ingot continuously formed in the mold. At least a portion of the guide is curved in such a manner that the strand is deflected from a generally vertical orientation to a generally horizontal orientation. A straightener is arranged at the end of the curved portion of the guide for the purpose of straightening the strand.
In the continuous casting of steel with a generally vertical open-ended mold, the lower or outlet end of the mold is sealed before the start of the cast so that the strand may have a chance to form. The sealing is accomplished by means of a dummy bar having a head which fits in the outlet end of the mold with little clearance. The dummy bar is flexible, e.g. composed of pivotally connected links, so that it may conform to the curvature of the strand guide. The dummy bar head is provided with means which enable the strand to become coupled with the dummy bar head so that, when the dummy bar is moved downwardly along the strand guide to unblock the outlet end of the mold, the strand is pulled along; In this manner, withdrawal of the continuously cast strand from the mold is initiated. Once withdrawal of the strand has been properly initiated, the dummy bar may be disconnected from the strand.
When the dummy bar head is in its sealing position, it is situated at the top of the dummy bar which, in turn, extends along the strand guide located below the mold. Normally, the dummy bar is positioned in this manner in one of two ways. Thus, it may be fed through the straightener and passed upwardly through the strand guide. On the other hand, it may be lowered through the mold. The latter procedure has the advantage that shorter preparation periods between two casts may be achieved.
A known arrangement for introducing a flexible dummy bar into the strand guide via the mold includes a transfer device which is movably mounted on the casting platform supporting the mold. The dummy bar is lifted from the strand guide to the casting platform when withdrawal of a strand has been initiated by the dummy bar. The latter is loaded onto the transfer device at a location spaced from the mold. Once casting of the strand has been completed, the transfer device lowers the dummy bar through the inlet end of the mold so that the dummy bar may be readied for the start of another cast.
The transfer device is provided with a horizontal roller table which is bounded on either side by a roller track in the form of a quarter of a circle. The dummy bar is loaded onto the horizontal roller table via one of the curved tracks by a cable winch. This cable winch is uncoupled from the dummy bar before introducing the latter into the mold and the dummy bar is then held by a pair of driven rollers. The rollers cause a frictional clamping force to exist between the dummy bar and the transfer device.
The clamping force has the disadvantage that the errors in positioning the dummy bar on the horizontal roller table and the errors in positioning the transfer device may be cumulative and consequently lead to difficulties during the introduction of the dummy bar into the mold. Thus, in spite of the fact that the dummy bar and its head are designed to fit in the mold cavity with a certain amount of play, it is not possible to avoid scratching the inner walls of the mold. In addition to this disadvantage of the transfer device, a difficulty arises from the relatively small, curved roller tracks connected with either end of the horizontal roller table and, in particular, from the curved roller track connected with that end of the horizontal roller table via which the dummy bar is introduced into the mold. This difficulty, which exists for flexible dummy bars composed of pivotally connected links, stems from the fact that the individual links tilt upon being displaced from the horizontal roller table onto the curved roller track. The tilting movements of the links cause the dummy bar to be fed into the mold in a jerky fashion and it is not possible to eliminate the possibility of damage to the inner walls of the mold. A further disadvantage of the transfer device resides in that the horizontal roller table has a length approximating that of the dummy bar and accordingly takes up a large amount of space on the casting platform.
Another known arrangement for introducing a flexible dummy bar into the strand guide via the mold also includes a transfer device having a roller table for the dummy bar. Here, the roller table is pivotable from a horizontal to a vertical orientation and is swung to its vertical orientation during loading of the dummy bar. A lifting mechanism which is independent of the roller table lifts the dummy bar from the strand guide to the level of the casting platform in such a manner that the dummy bar also has a vertical orientation. The dummy bar is then transferred to the vertically oriented roller table by hanging it on a hook which is provided on the roller table for this purpose. Subsequently, the roller table is rotated back to its horizontal orientation. The dummy bar is now moved over the roller table towards the mold via a finger which is driven by a chain drive and travels along the roller table. The finger is able to control the speed of the dummy bar during the introduction thereof into the mold.
The latter arrangement also has certain disadvantages. Thus, it is expensive, particularly because of the mechanisms which must be provided for rotating the roller table. Furthermore, the errors in positioning the roller table for the introduction of the dummy bar into the mold are relatively large due to the pivotal mounting of the roller table. Moreover, the roller table has a length approximating that of the dummy bar. As a result, the roller table again takes up a large amount of space on the casting platform.